Question

A 0.1025-g sample of copper metal is dissolved in 35 ml of concentrated hno3 to form cu2 ions and then water is added to make a total volume of 200.0 ml. (calculate the molarity of cu2.)

Answer 1

Molarity is defined as number of moles of solute in 1 L of solution.

Here, 0.1025 g of Cu is reacted with 35 mL of HNO_{3} to produced Cu^{2+} ions.

The balanced reaction will be as follows:

Cu+3HNO_{3}\rightarrow Cu(NO_{3})_{2}+NO_{2}+H_{2}O

From the above reaction, 1 mole of Cu produces 1 mole of Cu^{2+}, convert the mass of Cu into number of moles as follows:

n=\frac{m}{M}

molar mass of Cu is 63.55 g/mol thus,

n=\frac{0.1025 g}{63.55 g/mol}=0.0016 mol

Now, total molarity of solution, after addition of water is 200 mL or 0.2 L can be calculated as follows:

M=\frac{n}{V}=\frac{0.0016 mol}{0.2 L}=0.008 mol/L=0.008 M

Thus, molarity of Cu^{2+} is 0.008 M.